Silicon-on-insulator wafers are of considerable interest in microelectronics because they make feasible integrated circuits with low parasitic capacitances and improved isolation between circuit components. To achieve the maximum benefits of SOI, it is important that the silicon be of high quality, especially with respect to its crystal structure.
Various techniques have been proposed for growing high quality monocrystalline silicon-on-insulator, but none has proved completely satisfactory.
One of the techniques which has had some success involves an epitaxial-lateral-overgrowth (ELO) technique. In this technique, a monocrystalline silicon wafer has its top surface oxidized to form an insulator layer and this layer is then opened to expose regions of the silicon substrate to serve as seed holes. There then follows an epitaxial deposition of silicon to fill selectively the seed holes with vertically grown epitaxial silicon without deposition on the oxide and then without interruption to grow the silicon also laterally away from the filled hole and over the oxide layer as well as vertically. This technique has the disadvantages that the lateral overgrowth usually proceeds only so far before either silicon nucleation occurs on the oxide which interferes with the epitaxial lateral growth or the overgrowth becomes polycrystalline. Moreover, because of the seed holes, it is not completely SOI. In one form of this technique, the seed holes are placed very close together to reduce the possibility of nucleation before the lateral overgrowth merges to form the continuous silicon fill-in. A disadvantage of this technique is that because of the larger area of seed holes, the result is even less true SOI.